A medieval Portuguese timeline written by SteveW. You can read it here.
The PoD is that the siege layed to Moor-controlled Lisbon in July 1147 by Alfonso I. (the first Portuguese king) was more successful in its early stages. This lead to an earlier end of the siege, with Alfonso victorious and not suffering the OTL mutiny and loss of siege engines that he and his armies suffered as the siege dragged on for months, until October. A smoother capture of Lisbon eventually leads to different developments in the fledgling Portuguese monarchy.